As used herein, the term “integrated circuits” generally refers to monolithic semiconducting devices, such as those formed of group IV materials like silicon or germanium or mixtures thereof, or group III–V compounds such as gallium arsenide. The term “integrated circuits” includes all known configurations of such devices, such as memory and logic, and all designs of such devices, such as CMOS and bipolar.
Integrated circuits are typically formed through a series of photolithographic processes, where photoresist is applied across the surface of the substrate on which the integrated circuits are fabricated. The photoresist is exposed with a pattern that remains in the photoresist after it is developed. Processing is then accomplished in some manner through the voids that are formed in the patterned photoresist. For example, the exposed portions of the integrated circuits being fabricated can be etched, receive deposited layers, or be doped, such as with ion implantation.
An anti reflective coating is often placed on the substrate to improve various parameters, such as dimensional control, of the photolithographic process. This is accomplished by the antireflective coating reducing both the reflectance of the light off of the substrate and also the standing wave effects that are associated with such reflectance. Commonly used antireflective coatings are a class of non-photoactive organic materials.
The antireflective coating is typically spun onto the substrate in a manner that is similar to that used to apply photoresist. When this is done, the antireflective coating tends to build up on the edge of the substrate in a formation that is generally known as an edge bead. Because the edge bead can flake off and cause contamination and other problems with the integrated circuit fabrication process, it is generally removed using an organic solvent.
A typical edge bead removal process uses a swing arm dispenser to direct a spray of the edge bead removal solvent onto the edge of the substrate for a period of about five seconds. The typical process steps used are: (1) start the substrate rotation, (2) start dispensing the solvent through the spray nozzle, but not onto the substrate, (3) sweep the swing arm to move the spray nozzle and direct the solvent spray onto the edge of substrate, (4) Hold the spray nozzle at the desired edge bead removal set point for about five seconds, (5) move the spray nozzle back off of the substrate, stop dispensing the solvent through the spray nozzle, and (7) stop the substrate rotation. The nozzle is typically held so as to continuously direct the spray along a vector that is normal to the plane of the surface of the substrate.
Current edge bead removal processes are generally effective at removing the edge bead formation, but tend to result in a line of swollen and partially removed antireflective coating that circles around near the edge of the substrate along the interface between the solvent sprayed portion of the substrate and the portion of the substrate where the antireflective coating remains. This swollen ring of antireflective coating tends to remain even after the cleaning process is performed after the photolithography processing steps, because it is so thick. This circumferential residue of antireflective coating around the edge of the substrate creates what is known as the antireflective coating scar.
The scar tends to result in defects that reduce the yield of the integrated circuits on the substrate. The defects are caused when material such as an oxide or metal layer is deposited on top of the scar. In later steps, such as those involving thermal stress, the deposited material can flake off of the scar, because the thermal expansion coefficients are different, and the antireflective coating scar has generally poor adhesion properties. The scar can also cause defects by masking off material in subsequent etch processes, resulting in a stringer of unwanted material that can flake, peel, or short.
Some attempts have been made to remove the scar with extra processing, such as an edge etch to remove the films that are on top of the scar. However, this approach tends to create other issues, due to the cost of the extra processing steps. Most processes simply ignore the antireflective coating scar, and try to limit the extent of subsequent flaking defects by controlling later thermal processes, such as by using slower thermal ramps or lower temperatures. However, this approach is not completely effective, and tends to decrease the effectiveness of the processes that are modified in this manner.
What is needed, therefore, is a system that overcomes, at least in part, some of the problems described above.